The invention relates to a kit servomotor.
Servomotors consist of an electromotor and a device for measuring angular rotation, which in the following is referred to as a rotary encoder. The electromotor has a motor stator and a rotor, such that the rotary encoder measures the angle of rotation, or a rotor magnitude that is dependent on the angle of rotation, in relation to the motor stator or the motor housing. To this end, an encoder shaft belonging to the rotary encoder is coupled to the rotor of the electromotor, and a stator unit belonging to the rotary encoder is coupled to the motor stator. The coupling must create an isogonal connection that is as true as possible, in order to provide an exact angular measurement. At the same time, it must be able to accept the radial and axial alignment tolerances that are unavoidable with the installation of the rotary encoder on the electromotor.
Two basic variations are known for coupling the rotary encoder to the electromotor. In one design, the motor stator of the electromotor and the stator unit of the rotary encoder are firmly connected to each other, and the rotor of the electromotor and the encoder shaft are connected to each other with a coupling that is radially and axially flexible, but provides as much angular rigidity as possible, particularly a coupling in the form of a bellows connection. In another design, the rotor of the electromotor is firmly connected to the encoder shaft, and the motor stator and the motor stator unit of the rotary encoder are connected to each other over a stator coupling, which is often referred to as a torque support arm. The basic construction of the two designs is described, e.g., in DE33 10 564 A1.
For kit electromotors, the rotor is positioned in the motor stator without being mounted. The kit motor is made available for the given application as a unit consisting of the motor stator and the mounted rotor. Only when the kit motor is installed on the output side does the mounted rotor assume its operating position in the motor stator. For kit servomotors the result is that when the electromotor is mounted the rotary encoder coupled to the motor stator and the rotor must, in equalizing fashion, bridge over a relatively large radial and axial movement between the rotor of the electromotor rotor and the stator. This necessarily large degree of equalization of the radial and axial movements works against the need for the greatest possible isogonality in the configuration when mounted.
If, in a manner known to the prior art, the rotor of the electromotor and the encoder shaft are joined by means of a bellows connection, problems arise that are difficult to solve, particularly because, in the case of angular acceleration, the inertia of the rotating parts of the rotary encoder that are connected to the encoder shaft results in a torque which may cause resonance vibrations in the entire system. This is particularly a source of problems when a high normal rigidity is required in the servomotor system.
The known stator connection avoids this problem, since only the bearing friction of the rotating parts, which is minimal, exerts a torque on the stator connection. Thus practically no torque that is dependent on the rotational acceleration is exerted on the stator connection. However, in a configuration with a stator connection it can be difficult to minimize the mass of the rotary encoder system, and this can be problematic particularly when there are large diameters. The greater the mass of the rotary encoder system, the more rigid is the chosen stator connection, which in turn increases the forces at work on the bearings of the rotating parts of the rotary encoder, and this is disadvantageous for the operating life of the configuration.